Electrical fuse plug



July 11, 1933.

M. F. TUCKER ELECTRICAL FUSE PLUG Filed March 16, 1931 Qb8er0a71mu ZI/ndou) d 08W Acelaie.

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' unsuitable for this Patented July 11, 1933 UNITED STATES PATENT OFFICE 11111011 I. TUCKER, OF PBOVHJENCE, RHODE ISLAND, ASSIGN'OB TO EASTMAN KODAK comm, 0] ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK mnc'rmcan ros n rnue Application and March 16, 1931. serial 10. 522,935.

This invention relates to electrical fuse plugs havin windows or observation orifice covers of cel ulose acetate sheeting.

In the production of electrical fuse plugs it has been the practice for many years to place a window com osed of a thin sheet of mica on the top of said plugs for the purpose of permitting observation to be made as to the condition of the fuse wire within the plug. While mica hasbeen satisfactory from an electrical standpoint it has shown many disadvantages with reference to the utility of such plugs, among which ma be mentioned the low transmission of Hg t through the mica and its high reflective power, as well as, the great dispersion of light due to surface irregularities inherent in the highly developed cleavage which lepidolite, muscovite and other types of mica are known to possess. Also, because'of its high cost, mica has been purpose.

Recently fuse p ugs have been manufactured containing lass windows but these fuse plugs have the disadvantage in commercial use of extreme brittleness which leads to many broken windows in plugs of this type both in handling and in use. In neither of the types of fuss plug windows mentionedabove is there any means of ascertaining whether or not the fuse wire has been melted exce t by observation through the window whic is usually unsatisfactory because of the dee recess in the plug in which the fuse wire is p aced and the dark places in which fuse plu are usually located in use.

I ave found that cellulose acetate in sheet form of any desired thiclmess, for example, from .005 inches to inches may he successfully employed as windows forfuse plugs. The cellulose may contain admixed therewith plasticizers such as di-ethyl phthalate, ortho-cresyl-para-tolnene-sulfonate, benzo-phenone, or other materials imparting similar properties to cellulose acetate. If desired, other plastic materials such as gums, waxes, heavy metal soap, solid fatt acids, or a material which will cause the cel ulose acetate sheet to darken or hlacken upon decomposition by heating such, for instance, as cinnabar, flowers of sulfur, selenium salts,

etc., chlorinated hydrocarbons, such as chlorinated diphenyl etc. may be added to the cellulose acetate, if desired. It is understood, of

course, that the acetate itself will darken perceptibly due to hot metal which is thrown off by the fuse when being blown. 1' have found that the cellulose acetate sheet will withstand the action of heat caused by high current over considerable periods of time before the fuse is blown. I have also found that acetate sheets are much more transparent than mica when used in a similar situation, and that amperes was run through this plug, the fuse wire melted very rapidly and spattered with considerable force, but thecellulose acetate window-was quite unimpaired except. that it had darkened quite perceptibly.

In another instance two fuse plugs of the same 20 ampere rating were maintained at.

approximately 18 amperes for nearly two hours, during which time they reached a temperature of 150 F. and even higher. The current was then increased to 25 amperes and the fuse wire melted in one instance 25 minutes after the current had been inc eased, and the second in '35 minutes. These fuses,

after the fuse wire had melted, showed anunmistakable mark on the inner surface of the cellulose acetate window. Before the fuse wire had melted, the cellulose acetate window had shown much better light transmission than either the mica or the thick glass windows in similar plugs mentioned above. After the fuse wire had melted, the surface of the cellulose acetate window bore a mark produced by imbedding a portion of the molten metal of which the fuse wire was composed intothe cellulose acetatewindow.

This resulted in some plastic flow of the inner surface of the window as well as surface decomposition of the cellulose acetate so affected, darkeningthe acetate sheet in that locality giving an unmistakable signal of the blowing of the fuse.

In the accompanying drawing in which like reference numerals refer to like parts, a fuse plug is illustrated having a cellulose acetate window. Fig. l is a vertical section taken through the center of the fuse plug and Fig. H is a plan view thereof. The fuse plug is composed of the base or foundation 1 on which are located the terminals 2 and 3. Connecting these terminals is the fuse wire 4, with the customary area of high resistance. The window 5 composed of cellulose derivative shceting is held to the foundation of the plug by means of the annular ring 6.

It is understood that any thickness of sheet desired which admits of transparency may be used. However, for reasons of economy it is preferred that the sheeting be only thick enough to form a window which is fairly resistant to handling.

@ther fatty acid esters, of cellulose, especially the higher fatty acid esters or the mixed esters such as cellulose acetate-propionate, cellulose propionate-stearate, cellulose acetate-benzonate, cellulose hutyrate etc., or cellulose ethers such as ethyl cellulose may be used in this connection. Nitrocellulose can also be used, but it has the disadvantages of high inflammability and of possible darkening on long standing.

What ll claim as my invention and desire to secure by Letters Patent of the United States is:

mime? 1. An electrical fuse plug having an observation window of cellulose organic derivative sheeting in proximity to the fuse wire of the fuse plug.

2. An electrical fuse plug having an observation window of cellulose mixed organic ester sheeting in proximity to the fuse wire of the fuse plug.

3. An electrical fuse plug having an observation window of cellulose higher organic ester sheeting in proximity to the fuse wire of the fuse plug.

4. An electrical fuse plug havingcan observation Window of cellulose acetate sheetirig in proximity to the fuse wire of the fuse 5. An electrical fuse plug having an observation window which comprises a cellulose derivative and a material which darkens upon the blowing of the fuse.

6. An electrical fuse plug having an observation window which comprises cellulose acetate and a material which darkens upon the blowing of the fuse.

7. An electrical fuse plug having an observation window comprising cellulose acetate and a plasticizer.

8. An observation window for an electrical fuse plug comprising cellulose derivative sheetin which darkens at the temperature of melting of the fusible alloy.

9. An observation window for an electrical fuse plug comprising cellulose acetate and a material which darkens upon heating.

Signed at Providence, R. 1. this 9th day of March 1931.

MILTON F. TUCKER. 

